Thermodynamic Properties of Nd1+xBa2–x­Cu3Oy Compounds and Their Application for Optimizing the Synthesis of Superconducting Materials

Abstract

AbstractThe standard enthalpies of formation from oxides of Nd1+xBa2–xCu3Oy, where x = 0–0.8 and y = 6.65–7.24, were determined by using dissolution enthalpies of these compounds measured by solution calorimetry. The temperature dependence of the heat capacity of NdBa2Cu3O6.87 wasmeasured over the range 5–320 K by adiabatic calorimetry. The absolute entropy, S°(T), the enthalpy of heating, H°(T K) – H°(0 K), and the reduced Gibbs energy, Φ°(T) = S°(T) – [H°(T) – H°(0)]/T, were calculated by using the temperature dependence of Cp in the interval 0–320 K. The heat capacity and absolute entropy of NdBa2Cu3O6.87 over the temperature range 320–1380 K were estimated by methods of quantum chemistry with use of the temperature dependence of Cp at low temperatures. A thermodynamic simulation was performed on the basis of the obtained data, and the conditions for synthesis of the NdBa2Cu3O6.9 phase were determined.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)